What causes pH to rise?

[tim_pool_newbie]

I've been maintaining my new IG pool with the BBB method, and for the most part have had excellent results. My pH has consistently stayed around 7.5 - 7.6. However, this morning it seems to have spiked up to 8.2. I've just added the appropriate amount of pH Down (dry acid) to counter it, but I'm curious as to any thoughts on what would cause the sudden spike.

With a CYA level varying between 50-60, I've been targeting a FC level of 7. I have a very high chlorine demand during the day, I believe due to the wide open direct sunlight it receives all day. My CC level is always at zero and even overnight FC loss tests tell me that I have no algae issue to speak of.

Gearing up for a heavy bather load this weekend, and a low end of day FC reading yesterday of 2.5, I bumped my chlorine up to 10 last night, which is exactly what it measured this morning.

The only other anomaly is that my neighbor swam in the pool yesterday for an hour or two with his 2 young sons, and I had the waterfall going during that time. I know aeration can increase pH, but I've had that running for an entire weekend and never saw this high of a pH spike.

As I said, I've already added dry acid to correct this, but I'm curious what the cause might be - so I can be on the lookout in the future.

For full reference, here are my latest test results:

FC - 10
CC - 0
TC - 10
pH - 8.2
TA - 90
CH - 220
CYA - 50
Temp - 82
All taken this morning @ 9:30am

Thanks,
Tim

 

[dmanb2b]

Plaster curing, SWG, waterfall/aeration and TA at 90 which can be reduced to 60-70. Outside of that...you'll experience PH rise while the gunite is curing...probably a year or so. TA at 60-70 should help slow the rise down for you